Electroacoustic transducer



July 12, 1966 F. MAssA 3,260,990

ELEGTROACOUSTIC TRANSDUCER 2 SheetsSheet 1 Filed Jan. 5, 1962 f6 46 46I2 40 42 a 56 20 56 ATTORNEY.

July 12, 1966 F. MASSA ELECTROACOUSTIC TRANSDUCER 2 Sheets-Sheet 2 FiledJan. 5, 1962 IN VEN TOR.

ATTORNEY United States Patent 3,260,990 ELECTROACOUSTIC TRANSDUCER FrankMassa, Cohasset, Mass, assignor, by mesne assignments, to DynamicsCorporation of America, New York, N.Y., a corporation of New York FiledJan. 3, 1962, Ser. No. 164,010 14 Claims. (Cl. 340-12) This inventionrelates generally to improvements in electroacoustic transducers, andmore particularly to new and improved sonar transducers for generatinghighpower sound in very deep water at frequencies in the lower ormid-audible range. This invention is a continuation-in-part of myco-pending application, Serial No. 34,731, filed June 8, 1960.

One object of this invention is to provide an electroacoustic transducerof improved construction which is capable of generating acoustic powersof several hundred to several thousand watts and of operating atsubmerged depths down to many thousands of feet of water.

Another object of this invention is to produce a very rugged transducerof improved construction which is capable of operating at large, lowfrequency amplitudes of vibration sufficient to generate acoustic powerdensities of the order of 10 watts per square inch of radiating surface.

A further object of this invention is to still further reduce the weightof the radiating portion of the vibrating system of a high power sonartransducer in order to increase the band width of high efficiencyoperation of the transducer.

A still further object of this invention is to increase the efiiciencyof coupling between the radiating surface of a sonar transducer and thewater at high hydrostatic pressures without the need of any pressurerelease materials.

Another object of this invention is to produce an underwater transducerof improved construction which is capable of efficient operation in thelower or mid-audio frequency range.

Still another object of this invention is to provide a uniqueelectromagnetic transducer construction characterized by an inertia massflexibly suspended within and totally enclosed by a radiating mass whichforms the outer protective housing of the transducer.

Another object of this invention is to provide a new and improvedelectroacoustic sonar transducer with permanent magnetic polarizationsuch that high efficiency operation results in the lower or mid-audiofrequency range.

These and other objects of the invention are set forth withparticularity in the appended claims. However, for a betterunderstanding of the invention itself, together with further featuresand advantages thereof, reference is made to the accompanyingdescription and drawings in which are shown several illustrativeembodiments of the invention.

In the drawings:

FIGURE 1 is a vertical cross-section taken through an illustrativetransducer embodying one form of the invention;

FIGURE 2 is a sectional view taken substantially as shown along the lineZ-2 of FIGURE 1;

FIGURE 3 is an end or plan view of one illustrative type of foldedbaffle structure embodying another form of the invention;

FIGURE 4 is a sectional view taken substantially as shown along the line44 of FIGURE 3;

FIGURE 5 is a sectional view of a tunable folded baffle structureillustrating another embodiment of the invention; and

3,2003% Patented July 12, 1956 "ice FIGURE 6 is a sectional view takensubstantially as shown along the line 66 of FIGURE 5.

Referring now to the drawing, and more particularly to FIGURES l and 2thereof, the reference character 10 identifies a massive base structureof generally hemispherical shape and having a plane surface 14 at itsupper portion. A second relatively light structure 12, which for examplemay consist of an aluminum or magnesium alloy or the like, and which maybe further lightened, if desired, as by casting the aluminum into asponge-like mass which would reduce the effective density of thematerial without reducing its rigidity, is provided to serve as anadaptor plate. Preferably the adaptor plate 12 has a surface contouredto mate with the inner surface of the transducer housing hemisphericalshell 16. One surface 18 of adaptor plate 12, advantageously is machinedfiat so that it may be set parallel to the plane surface 14 of the heavybase 10.

In accordance with a feature of this invention, a stack of laminationsof magnetic material 20 is securely bonded, as by means of a suitablemetal-to-metal cement, such as one of the epoxies, to the plane face 18of adaptor plate 12. Another relatively massive magnetic assembly,comprising a number of cemented stacks of magnetic laminations 22 and24, is assembled to a set of permanent magnets 26. Permanent magnets 26may preferably be one of the sintered oxide types which develops highmagnetiz-ing forces through relatively thin sections, although thoseskilled in the art will appreciate that other types of magnets may beused. The magnets are preferably in the form of thin plates which act asseparators for the lamination stacks 22 and 24.

In accordance with the invention embodiment illustrated in FIGURES l and2, the magnets 26 are magnetized with alternating north and south poles,as illustrated in FIGURE 1. The alternate stacks of magnetic laminations22 and 24 interspersed with the permanent magnets 26 are cementedtogether and consolidated into a massive composite rectangular assembly28 which is securely cemented to the plane surface 14 of the massivebase 10. Advantageously, the height of the magnets 26 is less than theheight of the lamination stacks 22 and 24 so that after the elements areconsolidated into the assembly 28, a number of rectangular slots remainin the assembly within which coils of wire 30 may be placed, asillustrated in FIGURES l and 2.

FIGURE 2 shows a sectional plan view of the composite magnetic assemblyincluding a pair of coils 30 nesting within the slots defined by thelamination stacks, as above described. During the preparation of themagnetic assembly, it is preferable to consolidate the magnetic assembly28 which is bonded to the base 10 including the coils 30 with a rigidpotting compound so that there can be no relative vibrational motionbetween the coils 30 and the associated magnetic assembly.

The invention further comprises a number of spring members 32 which areaccurately machined such that their heights are equal. The springmembers 32 are assembled to both the plane surfaces 18 and 14,respectively of plate 12 and base 10, as by means of the studs 34 andnuts 36. The studs 34 are preferably fastened to the base member 10 andadaptor plate 12 by means of a suitable cement so that they will notbecome loose during operation of the transducer. Similarly, the nuts 36may be also coated with cement during the assembly in order that theywill not become loose during operation.

In accordance with the invention, the shape of the spring members 32 isdetermined by the desired stiffness which is required for establishingthe resonant frequency of the transducer. The total height of the springmemhers 32 is adjusted such that when the structure is assembled and themagnets are fully magnetized, the resulting air gap between the ends ofthe stacks 22 and 24, and the surface of the magnetic laminationassembly 20 is equal to the desired amount for eflicient operation. Ithas been found that a suitable air gap dimension to produce an eflicienttransducer may lie in the approximate range .010 to .020. Thesedimensions are, of course, not critical and are only given to illustratea typical range of values which are suitable for the practice of theinvention.

The adaptor plate 12 has a passageway 38, as illustratecl in FIGURE 1,which permits the installation of the insulated wires 40 to establishelectrical connection between the coils 30 and the terminals 42.

In order that the transducer may operate satisfactorily in very deepwater and not fail under the extremely high hydrostatic pressuresassociated With such depths, it has been found desirable to use a highpressure molded cable and terminal arrangement which is assembled withina rugged cylindrical shell 44 whose wall thickness is sufficient towithstand the high hydrostatic pressure. A pair of shouldered insulatingbushings 46 are placed through suitable clearance holes provided in thebottom wall of shell 44, as illustrated. The electrical terminals 42have shoulders which rest on the upper surface of the flanged insulators46, as shown. The conductors within the waterproof cable 47 are solderedto the terminals 42 as illustrated, after which a rubber compound 48 ismolded to fill and hermetically seal the region between the cable 47 andthe high pressure terminal assembly comprising the housing 44 and theinsulated terminals 42. It has been found in actual practice that amolded cable terminal construction as just described operatedsatisfactorily underwater in ocean depths in excess of 20,000 feet.

In order that the molded cable assembly may be conveniently attached tothe transducer, I have provided a cylindrical flanged metal bushing 50welded, as at 51, to an opening in the outer housing 16. A suitablerecess or shoulder 53 is formed in the wall of bushing 50 to receive themating flange portion of shell 44, as illustrated in FIGURE 1. Asuitable waterproof rigid cement, such as epoxy, preferably is usedbetween the surfaces of shell 44 and bushing 50 at final assembly inorder to establish a completely water tight, high pressure seal at thecable terminals.

In order to increase the efliciency of the transducer of this inventionand to obtain higher acoustic power output, it is a feature of thisinvention that the suspended inertial weight, represented by the basemember plus the magnetic assembly attached to its surface, be kept highwhereas the total vibrating mass represented by the outer housing andthe structure attached to the outer housing be kept low. Since thetransducer is designed to withstand high hydrostatic pressure, it isadvantageous to employ a convex shell for the outer housing which willresult in minimum weight for maximum strength. The illustrativeembodiment of FIGURE 1 comprises two hemispherical shells 16 and 52which are assembled to form a complete sphere, as by means of Weld 54. Apair of cylindrical collars 56 are welded to the hemispherical shells,as illustrated, in order to provide an outer cylindrical bearing surfaceparallel to the axis of vibration to permit mounting the transducer intobaflle structures as will be described hereinbelow.

Although in the illustrative embodiment of FIGURE 1, the outer housingof the transducer is in the form of a spherical shell having theattached outer cylindrical collars 56, those skilled in the art willappreciate that the cylindrical collars 56 could be incorporated intothe Wall of the hemispherical shell by a forming operation, if desired,to eliminate the welding of the auxiliary collars. Alternatively theouter housing may comprise a separate cylindrical central collar with adome-shaped cap fastened to each edge of the central collar.

FIGURES 3 and 4 illustrate one preferred embodiment for mounting thetransducer structure above described in a folded bafile arrangementcapable of providing highly satisfactory operation in deep water. Thebasic transducer unit above described is of the inertia type in whichthe outside surface vibrates as a Whole relative to the suspendedinertial mass which is contained within the interior of the cylindricalshell housing. The operation of this transducer is similar to thetransducer operation described in greater detail in my co-pendingapplication Serial No. 34,731 filed June 8, 1960. In this co-pendingapplication, in addition to the operation of the transducer, there isdisclosed a number of bafiie arrangements whereby the out-of-phasevibration from one surface of the 0scillating transducer housing issuitably delayed by various baffle configurations such that the delayedenergy is brought in phase with the energy radiating from the oppositetransducer face, thereby increasing the efliciency of operation.

In the illustrative embodiment of FIGURES 3 and 4, the cylindricaltubular member 58 has a number of brackets 60 attached to its innersurface, as by means of bolts 62 and nuts 64. Advantageously, rubberbumpers 66 are cemented to the face of the brackets 60, as shown, toisolate the vibrating transducer from the bafile structure. A rubbercovering, not shown, may be placed around the cylindrical periphery ofthe transducer such that the transducer will rest on a rubber sheetduring vibration and thus be able to move with respect to the inner wallof the cylindrical tube 58, during its operation.

In accordance with a feature of this invention, the cylindrical tube 58is reduced in diameter by the tapered funnel portion 68 which is coupledto a continuing smaller diameter tube 70. The smaller diameter tube 70is bent as shown, and returns to a second funneled section 72 which, inturn, terminates in a larger cylindrical portion 74. Advantageouslycylindrical portion 74 is made concentric with the smaller diametercylindrical tube 58. A hole 78 through the funneled section 72 providesfor the passage of the smaller diameter tube 70. A weld 76 serves toseal the clearance space between tube 70 and the hole 78 in section 72.If desired, several separating rods (not shown) may be welded betweenthe outer surface of cylindrical tube 58 and the inner surface ofcylindrical portion 74 to provide additional radial rigidity for theconcentric assembly. Whether the provision of such separating rods isdesirable will depend on the relative magnitude of the diameters of thestructures which are employed in the assembly. The area of theconcentric annular opening formed by the cylindrical portions 58 and 74is preferably made approximately equal to the area of the cylindricalopening of tube 58 into which the transducer is mounted.

Although the outer shape of the portion 74 of the baflle structure isillustratively shown in FIGURES 3 and 4 as a cylinder it will beunderstood that the shape of this section may take the form of a square,a hexagon, or any other geometric shape which permits a nesting of suchsections when it is desired to assemble a multiple array of thesestructures into a tight totally enclosed, composite area. When the outersurface of the cylindrical bafile portion 74 is made in the form of apolygon, the funneled section 72 will serve as an adaptor between thepolygon and the smaller diameter cylindrical tube 70. When the outerbafiie portion 74 is made in the form of a polygon, the area of theperipheral opening is preferably held at a value approximately equal tothe area of the opening of the inner tube 58.

The length of the signal path in the baflie is illustrated by the arrowM2 in FIGURE 3. This path preferably is made equal to approximately aone-half wavelength at the center of the frequency range over which thetransducer is to operate. Under these conditions the sound radiated fromthe rear of the transducer will offer maximum reinforcement to the soundradiated from the front surface of the transducer.

Those skilled in the art will appreciate that restricting the diameterof the tubular baflle in the embodiment described hereinabove results ina great advantage because of the small cross-sectional area which has tobe turned through 180 at the folded section. By reducing the diameter ofthe folded section of the tube, there is a reduction in the area of thesurface at the bend to thereby minimize any undesirable reflectionswhich would be set up between the folded surface and the transducer.Secondly, there is a reduction in the phase shift in the wave front asit passes through the smaller section around the 180 radius. Therestriction of the area of the baffie as illustrated will naturallyincrease the magnitude of the sound pressure through the reducedsection. For high power transducers operating in shallow water, thisconstruction may lead to increased cavitation and thereby limit thepower handling capacity of the transducer assembly. For deep water use,however, which is the primary objective of this invention, cavitationproblems are not present and no practical disadvantage of limitation inpower handling capacity will result by this improved construction.

In accordance with a further embodiment of this invention, the baffiestructure arrangement of FIGURE 4 may be made adjustable to permit thelength of the line to be tuned to selected frequencies, as desired. Anillustrative embodiment comprising this highly desirable tunablearrangement is shown in FIGURES 5 and 6 of the drawing.

As there shown, the bafiie structure is generally the same as thestructure of FIGURE 4 with the exception that the folded overcylindrical tube 70 is formed in two parts and is connected byadjustable means to permit the spacing between the parts to be varied ina selective manner. This is effected by means of a pair of couplingmembers 80 which are formed with internal threading engaging, right andleft hand respectively, on the ends of the cylindrical tube portions.Rotation of coupling members 80 to increase or decrease the spacingbetween the ends of the cylindrical tube portions is effected by thecylindrical spur gear 82 which is meshed with gear teeth on the outsideof coupling members 80 and positioned for rotation on the shaft 84having a bevel gear 86 at its remote end. Bevel gear 86 is meshed withgear 88 which may be rotated, manually or otherwise in any suitablemanner to tune the baffle arrangement to a desired frequency ofoperation.

While there has been shown and described a specific embodiment of thepresent invention, it will, of course, be understood that variousmodifications and alternative constructions may be made withoutdeparting from the true spirit and scope of the invention. Therefore, itis intended by the appended claims to cover all such modifications andalternative constructions as fall within their true spirit and scope.

What is claimed as the invention is:

1. The improvement of an electromagnetic transducer comprising a sealedhousing structure having positioned therewithin first magnetic means,adapted to be spaced from said housing structure, mounted fortranslatory vibration relative thereto, said first magnetic meanscomprising an assembly of magnetically conducting elements separated bypermanent magnets, second magnetic means secured to said housingstructure and positioned in operable relation to said first magneticmeans, said second magnetic means comprising a magnetic conductingstructure, said first and second magnetic means defining an air gaptherebetween with said permanent magnets creating a flux density in saidair gap, current coil means operatively associated with said magneticmeans, terminal means for supplying electrical current to said coilmeans, and spring elements attached between said first and said secondmagnetic means to hold said magnetic means in operable relationship toeach other whereby translatory vibration of the housing structure willbe of opposite phase to the translatory vibration of said first magneticmeans whenever alternating current is applied to the current coils.

2. The improvement of an electromagnetic transducer comprising a sealedspherical housing structure having positioned therewithin first magneticmeans adapted to be spaced from said housing structure mounted fortranslatory vibration relative thereto, said first magnetic meanscomprising an assembly of magnetically conducting elements separated bypermanent magnets, second magnetic means secured to the inner surface ofsaid spherical housing structure and positioned in operable relation tosaid first magnetic means, said second magnetic means comprising amagnetic conducting structure, said first and second magnetic meansdefining an air gap therebetween with said permanent magnets creating aflux density in said air gap, current coil means operatively associatedwith said magnetic means, terminal means for supplying electricalcurrent to said coil means, and spring elements attached between saidfirst and said second magnetic means to hold said magnetic means inoperable relationship to each other whereby translatory vibration of thehousing structure will be of opposite phase to the translatory vibrationof said first magnetic means whenever alternating current is applied tothe 'current coils.

3. The improvement of an electroacoustic transducer comprising thecombination of a massive base member including a plane surface, a firstmagnetic assembly comprising a magnetic structure, said magneticstructure being secured to said plane surface of said massive base, asecond magnetic structure, an adaptor plate having a plane surface,means securing said second magnetic structure to the plane surface ofsaid adaptor plate, a shell like housing structure, means for securingsaid adaptor plate to the inside surface of said shell-like housingstructure, spring means, means for securing said spring means to each ofsaid first massive base structure and said adaptor plate.

4. The improvement of an electromagnetic transducer assembly forproviding radiation of opposite phase from a pair of opposite end facescomprising a baffle structure defining a tubular member having two endopenings, a sealed transducer structure positioned at one of said endopenings and mounted for free vibration therewithin, a tapered regionadjacent each end opening of said tubular member whereby the diameter ofsaid baflie structure is reduced over a portion of its lengthintermediate said end openings, means folding over the reduced diameterportion of said baffie structure whereby the two end openings thereofare brought into approximate alignment, and selectively adjustable meansfor varying the spacing between the tapered regions adjacent each endopening of said tubular member to enable the selective tuning of thebaffle structure to the operating frequency of the transducer structure.

5. The improvement of an electromagnetic transducer assembly inaccordance with claim 4 wherein said selectively adjustable meanscomprises a coupling member threadedly coupled to each of said taperedregions and adapted to vary the spacing between said tapered regionsupon rotation of said coupling member.

6. The method for assembling an electroacoustic transducer assembly ofthe type having a baffie containing shell-like housing formed of twoseparate sections enclosing a vibratile structure comprising a pair ofrigid elements separated by a compliant member which comprises the stepsof attaching one of said pair of said rigid elements to the innersurface of one section of said shelllike housing to support the entirevibratile structure from said one section, mating the second portion ofsaid housing structure with the first portion of said housing structureto totally enclose said vibratile structure, sealing the mating surfacesof said housing structure portions to produce a continuous water-tightexternal surface, positioning the housing structure adjacent one endface of a foldable baflle structure of the type defining a tubularmember having two end openings, and varying the spacing of the tubularmember at a gap therein intermediate said two end openings toselectively tune the folded baflle structure to the operating frequencyof the transducer.

7. In an electromagnetic transducer for operation underwater at highpower levels, first and second magnetic means, spring elementsconnecting said first and second magnetic means for constrained relativetranslatory high amplitude vibrational movement thereof along a certainaxis, current coil means operatively associated with said magnetic meansfor producing said relative vibrational movement thereof, a sealed rigidhousing structure secured to said second magnetic means and disposed inspaced completely surrounding relation to said first magnetic means,said first magnetic means having a mass sufiieient in relation to thecombined mass of said second magnetic means and said housing structureto cause high amplitude vibrational movement of said housing structure,as a whole, along said axis in response to application of high amplitudealternating current to said coil means.

8. In an electromagnetic transducer as defined in claim 7, said sealedhousing structure having a generally eonvex surface over at least aportion of its radiating surface.

9. In an electromagnetic transducer as defined in claim '7, said sealedhousing structure being spherical in shape.

10. In an electromagnetic transducer as defined in claim 9, furthercomprising a cylindrical collar secured to the surface of said sealedhousing, and having an axis in alignment with said axis of vibrationalmovement.

11. In a transducer assembly, a bafile structure ineluding a tubularmember having first and second openings at opposite ends thereof, atransducer mounted for vibration within said first opening and havingoutwardly and inwardly directed faces for radiating sonic Waves ofopposite phase, said tubular member having a foldedover intermediateportion of reduced cross-sectional area with said first and second endopenings being adjacent each other and facing in the same direction, andsaid tubular member having a length such that radiation from said secondend opening is in phase with radiation from said outwardly directed faceof said transducer.

12. In a transducer assembly as defined in claim 11, one of said endopenings being arranged in generally concentric relation about the otherof said end openings.

13. In a transducer assembly as defined in claim 12, wherein saidtubular member has a wall opening therein through which saidintermediate portion thereof extends.

14. In a transducer assembly in accordance with claim- 12, wherein theeffective cross-sectional areas of said first and second end openingsare approximately equal.

References Cited by the Examiner UNITED STATES PATENTS 2,597,005 5/ 1952Kendall 340-R FOREIGN PATENTS 73 6,743 9/1932 France. 345,579 12/1921Germany. 457,552 3/1928 Germany. 692,146 6/ 1940 Germany.

CHESTER L. JUSTUS, Primary Examiner. KATHLEEN CLAFFY, Examiner. L. H.MYERS, J. P. MORRIS, Assistant Examiners.

4. THE COMBINATION OF AN ELECTROMAGNETIC TRANSDUCER ASSEMBLY FORPROVIDING RADIATION OF OPPOSITE PHASE FROM A PAIR OF OPPOSITE ENDSURFACES COMPRISING A BAFFLE STRUCTURE DEFINING A TUBULAR MEMBER HAVINGTWO END END OPENINGS, A SEALED TRANSDUCER STRUCTURE POSITIONED AT ONEEND SAID END OPENINGS AND MOUNTED FOR FREE VIBRATION THEREWITHIN, ATAPERED REGION ADJACENT EACH END OPENING OF SAID TUBULAR MEMBER WHEREBYTHE DIAMETER OF SAID BAFFLE STRUCTURE IS REDUCED OVER A PORTION OF ITSLENGTH INTERMEDIATE SAID END HOUSINGS, MEANS FOLDING OVER THE REDUCEDDIAMETER PORTION OF SAID BAFFLE STRUCTURE WHEREBY THE TWO END OPENINGSTHEREOF ARE BROUGH INTO APPROXIMATE ALIGNMENT, AND SELECTIVELYADJUSTABLE MEANS FOR VARYING THE SPACING BETWEEN THE TAPERED REGIONSADJACENT EACH END OPENING OF SAID TUBULAR MEMBER TO ENABLE THE SELECTIVETUNING OF THE BAFFLE STRUCTURE TO THE OPERATING FREQUENCY OF THETRANDUCER STRUCTURE.